Fixes #4746: Prevent PowerShell commands from hanging indefinitely

- Improved PowerShell command construction to use try-finally blocks for better completion handling
- Added timeout mechanism for PowerShell commands to prevent indefinite waiting
- Fixed variable scoping issue in TerminalProcess.ts
- Enhanced error handling for PowerShell sleep commands

The issue was caused by PowerShell commands with sleep delays not properly signaling completion to VSCode's shell integration, causing the extension to wait indefinitely for user input.

Author: roomote